Mining of plant-derived antimicrobials is the major focus at current to counter antibiotic resistance.This study was conducted to characterize the antimicrobial activity and mode of action of linalyl anthranilate(LNA)against carbapenemase-producing Klebsiella pneumoniae(KPC-KP).LNA alone exhibited bacteri-cidal activity at 2.5％(V/V),and in combination with meropenem(MPM)at 1.25％(V/V).Comparative proteomic analysis showed a significant reduction in the number of cytoplasmic and membrane proteins,indicating membrane damage in LNA-treated KPC-KP cells.Up-regulation of oxidative stress regulator proteins and down-regulation of oxidative stress-sensitive proteins indicated oxidative stress.Zeta po-tential measurement and outer membrane permeability assay revealed that LNA increases both bacterial surface charge and membrane permeability.Ethidium bromide influx/efflux assay showed increased uptake of ethidium bromide in LNA-treated cells,inferring membrane damage.Furthermore,intracel-lular leakage of nucleic acid and proteins was detected upon LNA treatment.Scanning and transmission electron microscopies again revealed the breakage of bacterial membrane and loss of intracellular ma-terials.LNA was found to induce oxidative stress by generating reactive oxygen species(ROS)that initiate lipid peroxidation and damage the bacterial membrane.In conclusion,LNA generates ROS,initiates lipid peroxidation,and damages the bacterial membrane,resulting in intracellular leakage and eventually killing the KPC-KP cells.

Aims: Leaf blight disease caused by Pantoea spp. reduces rice yields in numerous nations. However, the exact strategy to combat Pantoea spp. has yet to be determined. Bactronophorus thoracites is a promising source of natural antimicrobial agents due to their potential as a substrate to generate peptides with high antimicrobial activity. This study determined the effects of lactic acid fermentation using Lactobacillus casei ATCC334 as a starter culture on antimicrobial activity against rice pathogens, proximate composition, and amino acid profiles from B. thoracites crude extract. Methodology and results: Bactronophorus thoracites was washed and deshelled to collect the flesh and homogenised at 4 °C before freeze-drying. The freeze-dried samples were fermented with L. casei for 4 to 8 days at 37 °C. The antimicrobial activity, MIC and MBC were determined using a spectrometer. The fermented protein was subjected to proximate and amino acid analyses. The antimicrobial activity of fermented B. thoracites protein (FBTP) was significantly (p<0.05) decreased with the increased fermentation days (from 4 to 8 days). The antimicrobial activity was also increased when the glucose concentration increased from 2% to 3%. However, raising the glucose concentration to 4% decreased the antimicrobial activity. The antimicrobial activity was significantly (p<0.05) increased when the substratewater (S/W) ratio increased from 0.84% to 0.96%. The FBTP (4 days, 3% glucose concentration and 0.96% S/W ratio) showed high antimicrobial activity against Pantoea ananatis and P. stewartii. The MIC and MBC values for FBTP were 500 μg/mL and 250 μg/mL against P. ananatis and P. stewartii. The zones of inhibition value for FBTP were 16.0 ± 0.5 mm (1000 μg/mL) and 9.33 ± 0.57 mm (500 μg/mL) for P. ananatis, and 11.7 ± 0.61 mm (1000 μg/mL), 9.33 ± 0.58 mm (500 μg/mL) and 7.17 ± 0.77 mm (250 μg/mL) for P. stewartii. The proximate composition and amino acid profiles of the freeze-dried protein hydrolysate powder were characterised. FBTP produced a higher value of protein (61.56%) and ash (32.38%) and a lower value of total fat (0.273%) and carbohydrates (6.27%) than the B. thoracites crude extract. Total amino acid content was 39.480 g/100 g in B. thoracites crude extract and 155.442 g/100 g in FBTP. The essential amino acid glutamine was the most abundant in B. thoracites crude extract and methionine in FBTP. Conclusion, significance and impact of study This study showed that lactic acid fermentation could produce FBTP using L. casei with improved functional characteristics and as a source of a natural antimicrobial agent against rice pathogens.
Lactic Acid ; Anti-Infective Agents